1. Field of the Invention
The present invention relates to a method and an apparatus for detecting deterioration of a lightning arrester, which can accurately and simply detect the condition of deterioration of a zinc oxide type lightning arrester installed to an insulator assembly.
2. Description of the Related Art
In order to protect an insulator assembly insulatively supporting a power line such as power transmission line from a lightning strike and to prevent a power transmission line or the like from melting down due to follow current in the event of the lightning strike, a zinc oxide type lightning arrester is installed to the insulator assembly. As well known, the zinc oxide type lightning arrester is made by connecting in series a plurality of zinc oxide elements (non-linear resistor elements) having a non-linear voltage-current characteristic, putting the zinc oxide elements into a container made of an insulating material, and further insulatively covering them with a rubber, polymeric materials or the like.
Such a zinc oxide type lightning arrester is typically installed to the tower side of the insulator assembly, and a discharging electrode at the tip of the arrester is disposed opposite to a discharging electrode of the line side with the series air gap G therebetween. The zinc oxide type lightning arrester is normally separated from the power line by the series air gap G and normally is not directly applied with an operating voltage.
On the other hand, when applied with a high lightning surge voltage by the lightning strike, the zinc oxide type lightning arrester becomes conductive because of decreasing resistance of the zinc oxide elements, which causes a discharge across the series air gap to allow the lightning surge current to flow into the tower side, allowing the insulator assembly to be protected.
Since the zinc oxide type lightning arrester is installed to the insulator assembly, the arrester being normally separated from the power line with the series air gap, deterioration of the zinc oxide elements and/or polymeric housing due to continuous energizing with power frequency voltage will not occur, but a main cause of the deterioration would be partial damage of the zinc oxide elements due to excessive lightning surge operating duty. Therefore, the deterioration of the arrester cannot be detected by visual inspection.
As described in Japanese Patent No. 2,942,030, a deterioration detector for a lightning arrester has been developed that touches the terminals of the arrester with a pair of detecting terminals and measures the insulation resistance of the arrester to evaluate the deterioration condition of the arrester. However, this method may also detect the reduction in surface resistance on housing due to wetness and/or pollution of the housing surface of the arrester, and may not be able to discriminate the deterioration of the arrester itself from others, so this method has not been used in practice.
Further, as described in Japanese Patent No. 2,943,465, an apparatus for monitoring a lightning arrester for failure has been suggested, which includes a voltage generator connected in parallel to the arrester, an impedance to ground connected in parallel to the voltage generator and a capacitor connected in series to the impedance to ground, and monitors the arrester for failure by detecting current flowing in the arrester using CT, the current being caused by the voltage applied by the voltage generator.
However, this apparatus always needs to be in conjunction with the arrester to monitor the arrester for failure, and a current sensor such as CT needs to be included in the arrester. In order to implement this method, every lightning arrester needs to include equipment, such as a current sensor, which is not required for the function of the arrester itself, so this method also has not been used in practice for reasons of reliability and cost.